Biased magnetically operated electrical switches



Junev 1967 H. D. BRUNETTE ETAL 3,325,695

BIASED MAGNETICALLY OPERATED ELECTRICAL SWITCHES 2 Sheets-Sheet 1 FiledApril 5 2 H.1 1. lntlll'lu'lllllllllllliiillklll I, 1 I I.IIIIIIIIII-IIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIII IllllIIlII-llIIIIIIIIIIIIIIIIIHIIIIIIIIIII IIIIIIIIIIInIIIiIIIIIIIIIIIIII V..' I fl----l United States Patent f 3,325,695 lllllASEl) MAGNETICALLY OPERATEDELECTRICAL SWITCHES Henry D. Brunette, Milwaukee, and Roy I-Iyink,Wauwatosa, Wis, assignors to Cutler-Hammer, Inca, Milwaukce, Wis., acorporation of Delaware Fiied Apr. 5, 1963, Ser. No. 270,854 Claims.(Cl. 317155) This invention relates to magnetically operated switchesand relays having operating bias applied electromagnetically.

It is often desirable to vary the pick-up and drop-out voltages andcurrents of the device to suit a particular application. In the case ofreed switches and relays utilizing reed switches, the operating voltagesare adjusted by means of electromagnets or permanent magnets in thevicinity of the reed switches to provide a steady biasing flux. However,the application of a biasing magnetic flux in the usual manner affectssimultaneously and similarly both the pick-up and drop-out currents. Itis difiicult to vary the pick-up and drop-out currents independently orto adjust the difference between these currents.

It is therefore. an object of this invention to provide biasing meansfor magnetically operated switches by which the pick-up and drop-outpoints may be varied independently and the difference between thesepoints may be selectively adjusted.

It is a further object of this invention to provide such a biasing meanswhereby the operation of the switch can be made dependent upon thepolarity of the actuating flux or voltage.

These objects are accomplished by the application to a magneticallyoperated switch of a pulsating unidirec tional biasing flux, thecharacteristics of which may be selectively adjusted to obtain thedesired operating characteristics for the switch.

Other objects and advantages of this invention will become apparent uponreference to the following description and accompanying drawings.

While the devices hereinafter described are adapted to fulfill theobjects stated, .it is to be understood that it is not intended that theinvention be confined to the particular embodiments disclosed since theyare susceptible of various modifications without departing from thescope of the claims.

Referring to the drawings:

FIGURE 1 shows an electromagnetic switching device which may be used inthe invention hereinafter described and claimed;

FIG. 2 shows a second version of electromagnetic device which may beincorporated in the present invention;

FIG. 3 is a graph of typical operating curves for prior art deviceswhich is useful in the expianation of the operation of this invention;

FIG. 3a is a diagram of a circuit for applying a bias voltage to obtainthe curves shown in FIG. 3;

FIG. 4 is a graph of operating curves for a device incorporating thepresent invention;

FIG. 4a is a diagram of a bias supply circuit which, when applied to thedevices of FIG. 1 or FIG. 2, forms an embodiment of the presentinvention and which yields the curves shown in FIG. 4;

FIG. 5 is a graph of another set of curves for a variation of theinvention; and

FIG. 5a is a diagram of a variation in bias supply circuitry, theoperating curves of which are illustrated by FIG. 5.

In FIG. 1 there is shown an electromagnetic device comprising a reedswitch 2, a bias coil 4, a magnetic shield 6 and an electromagnet 8.Reed switch 2 is of conventional construction having a sealed gas filledglass Patented June 13, 1967 envelope 2a. The magnetic reeds 2b and 2care attached, respectively, to terminals 2d and 22 which are sealed inthe ends of glass envelope 2a. Reed switch 2 is preferably shown withreed 2b shorter than reed 20 which places the contact gap toward thelower end of the switch. When magnetic flux of sufiicient intensity isimpressed upon switch 2, magnetic reeds 2b and 2c are mutually attractedand the gap between them closes to complete an electric circuit betweenterminals 2d and 2e. Exterior conductors (not shown) may be attached toterminals 2d and 2e.

Bias coil 4 surrounds reed switch 2 and comprises a single continuouselectrical wire winding 4:: covered by electrical insulating material 4band having terminals 40. Surrounding the lower end of coil 4, there is ashield 6 made of magnetic material which serves to shield the lower endof switch 2 from magnetic flux sources other than those directly belowterminal 2d.

Reed switch 2 is actuated by flux from a separate electromagnet 8 havinga magnetic core 8a, a coil 8b and terminals 80. A signal current appliedto terminals 8c serves to energize electromagnet 8.

FIG. 2 illustrates a variation of the electromagnetic device of FIG. 1.Certain elements of this second form are, for the sake of simplicity,given reference numerals identical to those of their equivalents in thefirst form illustrated in FIG. 1. Reed switch 2 is in this variationsurrounded by two coils, a bias coil 4 similar to that of FIG. 1 and asignal coil 10 having a winding 10a, terminals 10b and an electricallyinsulating cover 100. Signal coil 10 serves the same function aselectromagnet 8 of FIG. 1 in that coil 10 provides the actuating fluxfor reed switch 2 when a signal current is applied to terminals 10b.

Three sets of curves, one for each of three types of biasing current,are illustrated in FIGS. 3a, 4a and 5a. The pick-up and drop-out curves,labeled respectively PU and D0 are drawn on graphs of signal current (inmilliamperes) versus bias current in milliamperes. It may be assumedthat the direction of signal current is defined as forward when itseffect is additive to the biasing flux and is defined as reverse whenits effect opposes the biasing flux. FIGS. 3b, 4b and 5b show biascurrent supply circuits which will produce the results illustrated bythe corresponding curves of FIGS. 3, 4 and 5.

FIG. 3a illustrates the operating characteristics of prior art devicesand is useful in describing by contrast the operation and advantages ofthe present invention. Curves of the type shown in FIG. 3a are obtainedfrom biased relays having an unfiuctuating biasing force such as thatprovided by winding 4 when supplied by a source of steady DC. as shownin FIG. 3b. Steady DC. from source 12 is applied to terminals 40 of biascoil 4 to provide a biasing flux to reed switch 2. Variable resistance13 is serially connected with source 12 to selectively vary the level ofbiasing current and to provide the desired level of unfl-uctuatingbiasing flux. It can be seen that a steady biasing flux such as thatprovided by the circuit of FIG. 315 could also be supplied by apermanent magnet (not shown) rather than electromagnetic coil 4.

To illustrate the meaning of the operating characteristic curves, theoperation of a relay under different conditions will be first explainedwith reference to FIG. 3a. Assume that no bias current is applied tocoil 4 and initially there is no signal current. A signal current isthen applied in the forward direction to terminals 8c or 10b andincreased until the pick-up c-urve PU is intersected at approximately 40ma. at which point the contacts 2b and 2c close. As the signal currentis decreased, the contacts 2b and 20 remain closed until the drop-outcurve D0 is reached at approximately 13 ma, where contacts 2b and 20open. Similarly, if a signal current of the opposite polarity or thereverse direction is applied, the

curves of the lower or reverse half of FIG. 3a indicate that contacts 2band 2c will pick up at approximately 40 ma. and drop-out atapproximately 13 ma.

Next assume that an unfluctuating D.C. bias current of 8 mat. is appliedto coil 4 so that the relay operates along the vertical dashed line ofFIG. 3 at 8 ma. and that, with no signal current, point A represents thecondition of the relay. As a forward signal current is applied andincreased, the operating point representative of the state of the relayproceeds upwardly along the dashed line. Contacts 2b and 2c remain openuntil the pick-up curve PU is reached at point B where contacts 2b and2c close. At all points above the upper pick-up curve PU the contactsremain closed. As the signal current is reduced the contacts remainclosed until point C on the drop-out curve D is reached where thecontacts open. Upon a reversal of the signal current the operating pointpasses through point A and proceeds downwardly with increased reversesignal current. Contacts 2b and 20 remain open until point D on thelower pick-up curve is reached. At all points below the lower pick-upcurve the contacts remain closed. As the signal strength is reduced, thecontacts remain closed until point E on the drop-out curve is reached.

It can be seen that the effect of the bias current is additive to thatof forward signal currents and that the pick-up and dropoutcharacteristic curves therefore slope downwardly with increased biasingcurrents. A relay biased in the manner described is sensitive to thepolarity of the applied signal current under certain circumstances. Forinstance, reference to FIG. 311 will show that the relay when biasedwith a current of 8 ma. will pick-up when subjected to a forward signalcurrent of 40 ma. but will not pick-up when a signal current of the samemagnitude but opposite polarity is applied.

It should also be noted that the curves for the prior art device in FIG.3a substantially parallel one another and that the signal currentdiflerential between pick-up and drop-out is practically constantregardless of the bias current. Further, the magnitudes of signalcurrent required for pick-up and drop-out cannot be variedindependently.

Operating characteristic curves of the type shown in FIGS. 4a and 5a areobtainable from relays incorporating the present invention. FIG. 4aillustrates typical curves for a relay biased with a full wave rectifiedcurrent from a rectifying bridge 16 as shown in FIG. 4b. Alternatingcurrent, preferably of 60 cycles per second, from source 14 is rectifiedby the full wave bridge 16 consisting of diodes 16a. 16b, 16c and 16d tosupply to terminals 4c a pulsating full wave rectified current of theusual and well known wave form. Variable resistance 17 is seriallyconnected with coil 4 so that a biasing current of the desired magnitudemay be supplied to coil 4.

Consideration of the effects of several magnitudes of pulsating biasingcurrent will serve to clarify the meaning of the curves shown in FIG.4a. With zero bias current the operating points of the relay are, ofcourse, the same as the operating points at zero bias current in FIG.3a. With Zero signal current and a bias current of 8 ma., point Frepresents the state of the relay. As a forward signal current isapplied, the point representative of the state of the relay movesupwardly until at point G the relay picks up. At all points above pointG the contacts 2b and 2c remain closed. When the signal current isreduced, the relay drops out at point H. Similarly, with a reversesignal current, the relay picks up at point I and drops out at point K.It should be noted that the differential between the pick-up anddrop-out points decreases with increased bias current. Further, theforward drop-out current remains relatively constant with changes inbias level in comparison with the curve of FIG. 3a. With a reversesignal current, it is the pick-up current which remains relativelyconstant.

At higher bias current levels, due to the pulsating nature of thebiasing current, the contacts tend to open and close in a vibratoryfashion under certain conditions. The crosshatched areas labeled VIBrepresent the areas in which this vibratory phenomenon occurs. FIG. 4abest illustrates typical relay operation in the vibratory regions. At abias level of 16 ma., increase of the forward signal current will causethe relay to pick-up at point L without vibration. As the signal isdecreased from point L the contacts 2a and 2b remain closed until, atpoint N, they begin to vibrate and open intermittently. As the signalcurrent is further decreased, the vibration continues through thevibration area VIB until, at point P, the contacts remain open withoutintermittent closure caused by vibration of the contacts.

At slightly higher levels of bias current, a somewhat different type ofoperation occurs. For instance, at a bias current of 20 ma. when thesignal current is increased in the forward direction above the zerolevel, the contacts remain open until a dashed line within the vibrationarea VIB is intersected at point Q. At point Q, the contacts approachone another to the extent that they intermittently ciose in a vibratoryfashion. As the signal is further increased the contact continues tovibrate until at point R the vibration ceases and the contacts remainclosed. If the vibration area VIB is approached from above point R, thedecrease in signal current will cause the contacts to begin to vibrateopen at point R. They will continue to vibrate when the signal currentis further decreased through the vibration area VIB until point S isreached where the contacts remain open.

In the lower half of FIG. 4a, the vibration area VIB for reverse signalcurrents is inverted but is otherwise similar to that for forward signalcurrents.

FIG. 5a illustrates the effect of greater irregularity in bias currentsuch as that provided by the half wave rectifier of FIG. 5b. The source14 again preferably provides a cycle per second alternating current.Rectifying diode 18 blocks alternate half cycles to furnish a half waverectified current of well known wave form to terminals 4c. The magnitudeof the rectified current may be selectively varied by variableresistance 19 in series with coil 4. The most significant effect of thedecreased smoothness of wave form is that the pick-up curves PU and thedrop-out curves, DO, approach each other more rapidly as the biascurrent is increased. Consequently, as FIG. 5a shows, the operation ofthe relay with half wave bias current is substantially the same as thatshown in FIG. 4a for full wave bias current except that the similareffects of the pulsations in bias current occur with approximately halfthe average bias current required in FIG. 4a.

We claim:

1. A magnetically operated electrical switch assembly comprising:

electrical contact means having open and closed operating positions;

magnetic means energizable by application of magnetic flux to actuatesaid contacts;

a source of substantially steady magnetic flux applied to said magneticmeans, said source of steady magnetic flux being energizable foroperating said contacts between said operating positions;

a source of pulsating magnetic biasing flux applied to said magneticmeans for urging said contacts toward one of said operating positionsbut of a magnitude insufficient alone to cause operation of saidcontacts, the strength of said source of pulsating flux being selectedto cause operation of said contacts at a desired level of energizationof said source of steady magnetic flux.

2. A magnetically operated electrical switch assembly comprising:

a magnetically operated switch of the reed switch type having contactsmechanically biased to an open position and magnetic means for actuatingsaid contacts to a closed position upon application of sufiicientmagnetic flux to said magnetic means;

a source of substantiall steady magnetic flux for application to saidmagnetic means, said source of steady magnetic flux being energizablefor actuating said contacts to the closed position;

a source of pulsating magnetic biasing flux for application to saidmagnetic means of a magnitude insufficient alone to cause closure ofsaid contacts;

the strength of said pulsating magnetic biasing flux being selected tocause activation of said contacts at a desired level of energization ofsaid source of steady magnetic flux.

3. A magnetically operated switch assembly comprisa magneticallyoperated switch of the reed switch type having contacts mechanicallybiased to an open position and magnetic means for actuating saidcontacts to a closed position upon application of sufiicient magneticfiux to said magnetic means;

a source of substantially steady magnetic flux for application to saidmagnetic means, said source of steady magnetic uux being energizable foractuating said contacts to the closed position, the level ofenergization of said source of steady flux at which said contacts closebeing the pick-up point and the level of energization of said source ofsteady flux at which said contacts open being the drop-out point; and

a variable source of unidirectional pulsating magnetic biasing flux forapplication to said magnetic means of a magnitude insuflicient alone tocause closure of said contacts, variation of the strength of saidpulsating biasing flux when the polarity of said pulsating biasing fluxand said steady .fiux are of the same polarity, causing the pick-uppoint to decrease with an increased level of pulsating biasing fluxwhile the drop-out point remains substantially constant, and

variation of the strength of said pulsating biasing flux when saidpulsating biasing flux and said steady flux are of opposite polarity,causing the drop-out point to decrease with an increased level ofpulsating biasing flux While the pick-up point remains substantiallyconstant.

4. The invention as defined in claim 3 in which said source ofunidirectional pulsating biasing flux comprises a coil supplied withelectrical current from the unfiltered output of a half-wave rectifier.

5. The invention as defined in claim 3 in which said source ofunidirectional pulsating biasing flux comprises a coilsupplied withelectrical current from the unfiltered output of a full-Wave recifier.

References Cited UNITED STATES PATENTS 1,711,663 5/1929 Van Der Bijl 3172,721,297 10/1955 Estelle 317155.5 X 2,835,734 5/1958 Fisher 317155.5 X2,892,133 6/1959 Huge 317-156 X 3,088,056 4/1963 Tevonian 317- X3,100,091 8/1963 Mindheim et al. 317156 X 2/1965 Goldstcin 317155.5

1. A MAGNETICALLY OPERATED ELECTRICAL SWITCH ASSEMBLY COMPRISING:ELECTRICAL CONTACT MEANS HAVING OPEN AND CLOSED OPERATING POSITION;MAGNETIC MEANS ENERGIZABLE BY APPLICATION OF MAGNETIC FLUX TO ACTUATESAID CONTACTS; A SOURCE OF SUBSTANTIALLY STEADY MAGNETIC FLUX APPLIED TOSAID MAGNETIC MEANS, SAID SOURCE OF STEADY MAGNETIC FLUX BEINGENERGIZABLE FOR OPERATING SAID CONTACTS BETWEEN SAID OPERATINGPOSITIONS;